Members of an R2R3-MYB transcription factor family in Petunia are developmentally and environmentally regulated to control complex floral and vegetative pigmentation patterning Nick W. Albert 1,2,* , David H. Lewis 1,* , Huaibi Zhang 1 , Kathy E. Schwinn 1 , Paula E. Jameson 3 and Kevin M. Davies 1 1 New Zealand Institute for Plant and Food Research Limited, Private Bag 11-600, Palmerston North, New Zealand, 2 Institute of Molecular BioSciences, Massey University, Private Bag 11-222, Palmerston North, New Zealand, and 3 School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand Received 13 August 2010; revised 16 November 2010; accepted 13 December 2010; published online 14 January 2011. * For correspondence (fax +64 6 3517050; e-mail nicholas.albert@plantandfood.co.nz; david.lewis@plantandfood.co.nz). SUMMARY We present an investigation of anthocyanin regulation over the entire petunia plant, determining the mechanisms governing complex floral pigmentation patterning and environmentally induced vegetative anthocyanin synthesis.DEEP PURPLE (DPL) and PURPLE HAZE (PHZ) encode members ofthe R2R3-MYB transcription factor family that regulate anthocyanin synthesis in petunia, and control anthocyanin production in vegetative tissues and contribute to floral pigmentation. In addition to these two MYB factors, the basic helix–loop–helix (bHLH) factor ANTHOCYANIN1 (AN1) and WD-repeat protein AN11, are also essentialfor vegetative pigmentation.The induction of anthocyanins in vegetative tissues by high light was tightly correlated to the induction of transcripts for PHZ and AN1. Interestingly, transcripts for PhMYB27, a putative R2R3-MYB active repressor,were highly expressed during non-inductive shade conditions and repressed during high light. The competitive inhibitor PhMYBx (R3-MYB) was expressed under high light, which may provide feedback repression. In floral tissues DPL regulates vein-associated anthocyanin pigmentation in the flower tube, while PHZ determines light-induced anthocyanin accumulation on exposed petal surfaces (bud-blush). A model is presented suggesting how complex floral and vegetative pigmentation patterns are derived in petunia in terms of MYB, bHLH and WDR co-regulators. Keywords: anthocyanin,MYB, bHLH, transcription factor, petunia. INTRODUCTION Anthocyanins are coloured products ofthe flavonoid bio- synthetic pathway,produced in response to a range of developmentaland environmentalsignals. In flowers and fruits, they provide visual cues to pollinators and seed dis- tributors (Grotewold,2006).In vegetative tissues, they are frequently produced in response to stress. Anthocyanins are now generally accepted to be important photoprotectants, although their modes of action in vegetative tissues are still debated as they both absorb lightand are also powerful antioxidants (Steyn et al., 2002; Gould, 2004). It may be that anthocyanins have multiple physiological roles in vegetative tissues, or that their roles vary between species. Some plants lack anthocyanins,and presumably achieve photo- protection through alternative mechanisms,for example through non-flavonoid phenolic compounds (such as hydroxy cinnamic acid derivatives). Given both their importance as stress-responsive com- pounds in vegetative tissues and their ability to absorb photosynthetic light, the production of anthocyanins needs to be tightly regulated to achieve a balance between photoprotection and light harvesting. The flavonoid biosyn- thetic pathway is the bestcharacterised secondary meta- bolic pathway in plants (Figure 1), and much is now understood of its regulation. The primary point of regulation for anthocyanin biosynthesis occurs atthe transcriptional level, and several regulators of anthocyanin metabolism have been identified (Cone et al., 1986; Paz-Ares et al., 1986, 1987;Ludwig et al., 1989;Goodrich et al.,1992;de Vetten et al., 1997;Quattrocchio et al.,1998,1999;Walker et al., 1999;Borevitz et al.,2000;Spelt et al., 2000,2002;Carey et al.,2004;Schwinn et al.,2006).In all species studied to date,anthocyanin and proanthocyanidin regulation is con- ª 2011 The Authors 771 The Plant Journal ª 2011 Blackwell Publishing Ltd The Plant Journal (2011) 65, 771–784 doi: 10.1111/j.1365-313X.2010.04465.x